The present invention relates generally to the field of heat exchangers for automotive vehicles, and particularly to a heat exchanger fin that increases heat exchanger efficiency.
Air-cooled fin-type heat exchangers for automobiles are very well known. They are used for reducing the temperature of various working fluids, including engine coolant, engine lubricating oil, air conditioning refrigerant, and automatic transmission fluid, among others. The heat exchanger typically includes a plurality of spaced fluid conduits or tubes connected between an inlet and an outlet, and a plurality of heat exchanging fins interposed between adjacent conduits. Air is directed across the fins via a cooling fan or the motion of the automobile. As the air flows across the fins, heat in the fluid flowing in the tubes is conducted through the walls of the tubes into the fins and transferred or xe2x80x9cexchangedxe2x80x9d into the airflow.
One of the primary goals in heat exchanger design is to achieve the highest possible thermal efficiency. Thermal efficiency is measured by dividing the amount of heat that is actually transferred by the heat exchanger in a given set of conditions (amount of airflow, temperature difference between the air and fluid, etc.) by the theoretical maximum possible heat transfer under those conditions. An increase in the rate of heat transfer, therefore, results in greater thermal efficiency. Improved heat transfer can be realized by forming the fins and/or louvers on the fins at a predetermined angle in a manner also well known in the art.
Heat transfer is also affected by the air pressure drop associated with the change in airflow direction caused by the fins and louvers. A greater air pressure drop results in less heat transfer. Various types of fin and louver designs have been disclosed in the prior art with the object of increasing the heat exchanger efficiency by making improvements in the fins, louvers, and airflow pattern.
Examples of these prior art fin and louver designs include the staggering of fin rows in order to increase the amount of air encountered by the heat exchanger. Some designs have fin and louver assemblies manufactured at different angles determined by the amount of airflow through each louver. Other designs include louvers formed at an angle to the fin wall, rather than square to the fin wall. Still other designs vary the cross-section of the fins and louvers. All of these prior art designs, however, have heat exchanger fins that are symmetrical across their entire length. Further, the prior art discloses heat exchangers with multiple changes of airflow direction. In the prior art, air flows through the louvers until it reaches a middle transition piece. There the air changes direction and flows through louvers until it exits the heat exchanger.
The art continues to seek improvements. It continues to be desirable to increase overall heat exchanger efficiency. Fin design continues to play an important role in increasing heat exchanger efficiency.
The present invention concerns an apparatus for increasing heat exchanger efficiency by utilizing a novel fin design that is not symmetric across its entire length and has only one change in airflow direction. As noted above, the prior art discloses cooling tube fin louvers that are manufactured at a predetermined angle to the fins and are symmetric across their entire length when viewed from either its horizontal or vertical centerline. The angle of the louvers to the fin axes in the prior art remains constant (regardless of the cross-section of the louver) throughout the length of the fin element. Unlike the prior art, the present invention louvers are twisted at a midpoint, so that when viewed along a horizontal centerline, an X-shaped cross-section is observed. The twist separates the louver into two portions, with a resulting angle formed between the portions, as viewed in the X-shaped cross-section.
The angle formed between the portions of the louver on either side of the twist, however, is not limited to any particular value. The angle between the portions of the louver formed by the twist should be appropriate to the requirements of the heat exchanger. The angle between the portions, therefore, could be acute, perpendicular, or obtuse.
The twist in the louver allows each portion of the louver to maintain and direct airflow in a single direction, with only one change of direction, for minimum pressure drop. Air flows through the first set of louvers, then enters the next stage of fins, then the next, until it exits the heat exchanger. The air changes direction only oncexe2x80x94when it enters the heat exchanger through the first louvers, thus an improvement in airflow is obtained. The air is able to absorb more heat without a loss of efficiency via a pressure drop. As noted above, prior art heat exchangers disclose multiple air direction changes through the louvers. Every change in airflow direction causes a corresponding, and undesirable, pressure drop, which resulted in less heat transfer and, therefore, less efficiency. As a result of the single change in airflow direction with the twisted-louver high performance heat exchanger fin of the present invention, a decreased pressure drop across the heat exchanger is realized, as is an increase in heat exchanger efficiency.
Many benefits can be gained by utilizing the heat exchanger fin of the present invention. A heat exchanger may be made of a smaller physical size than prior art heat exchangers with the same cooling capacity, thus saving weight. Conversely, the heat exchanger could be made the same physical size and the electric motor used to drive the cooling fan could be sized smaller because of the greater efficiency of the heat exchanger. This could reduce the required voltage capacity of the vehicle""s electrical system, since the cooling fan motor is often the largest electric load in the vehicle. In addition, the twisted-louver high performance heat exchanger fin is no more expensive to manufacture than traditional type louvers, and is in fact cheaper to manufacture than staggered row fin louvers or fin louvers with varying angles of attack.